Books
I am a librarian in a middle school, and one of the things that I notice about good readers is that they miss so many wonderful books because these books are below their reading level. Most students are required to read on their level not below, and if they read well quickly, they never get the chance to read some of the best kid's books. While I think students need to be challenged, I also think that reading is beneficial no matter the level. Instead of reading one book, why not have the students read an easier series of books over a certain period of time OR several books by one author. They can present a book talk/author talk to the class or make a display for the library. (Books on the fifth grade level that I think would be good include a series by Barron. There are five books called The Early Years of Merlin--fantasy based on Merlin's childhood.) Your librarian could help you with more. (Reading level of 5+ Lewis's Narnia Chronicles, Jacque's Redwall series, Wrede's Talking to Dragon series, Stewart and Riddell's Edge Chronicles. etc.)
Get a list of Newberry Award books or any other award winning books. Have students check off what they have read and then read those they have not. The level may be easy for them, but they will be reading outstanding books.
There are suggested reading lists all over the internet. I'm sure your librarian would be willing to make some suggestions and help you with this.